1. Field of the Invention
This invention relates to a vascular dilatation instrument for use in curing a stricture or stenosis portion inside a blood vessel by dilating the stricture for improving blood flow to the peripheral side of the stricture. It also relates to a catheter intended to insert into fine blood vessels, for example, brain and heart vessels for curing and inspection purposes.
2. Prior Art
For curing a stenosed vessel by arterial sclerosis or the like, percutaneous transluminal coronary angioplasty (PTCA) has heretofore been practiced in the art wherein a catheter having a dilator at its distal end is inserted into the vessel until it reaches the stenosis and the dilator is inflated to dilate the stenosis for improving blood flow to the peripheral side thereof.
Known catheters with a dilator include those of the over-the-wire type wherein a guide wire is movable back and forth within a catheter as typified by that disclosed in U.S. Pat. No. 4,323,071 and those of time on-the-wire type wherein a catheter is fixed to a guide wire as typified by that disclosed in U.S. Pat. No. 4,573,470.
The demand for introducing vascular dilatation instruments into finer blood vessels is increasing year by year. There is a need for a vascular dilatation instrument which can be introduced into a finer or more peripheral blood vessel.
Currently available are vascular dilatation instruments and catheters of the over-the-wire and on-the-wire types both using a superelastic metal tube. These instruments are fully effective in transmitting translational and torsional forces (pushing force and torque) from the proximal end to the distal end of the instrument.
However, vascular dilatation instruments of the over-the-wire the-wire type can be folded at an angle where the superelastic metal tube terminates, that is, near the distal end of the superelastic metal tube. Vascular dilatation instruments of the on-the-wire type suffer from a loss of flexibility at their distal portion because the tubular member is entirely formed of a superelastic metal tube. Although attempts were made to render the distal portion flexible, none of them succeeded in providing flexibility as available with resins probably because of the superelastic metal tube.
Therefore, an object of the present invention is to provide a novel and improved vascular dilatation instrument which is effective for transmitting translational and torsional forces, which has a fully flexible distal portion and a highly stiff body portion, which prevents angular bending due to a change of physical properties at the interface between the stiff body portion and the flexible distal portion, and which is convenient to manipulate.
Conventional catheters to be inserted into blood vessels, for example, angiographic catheters and catheters for administering medicament into vessels are made of relatively flexible thermoplastic resins. One recent design includes a rigidity imparting member in the form of a metal wire (often a stainless steel wire) disposed around the catheter for preventing angular bending or collapse of the catheter and improving torque transmission while maintaining a flexible state.
With the recent advance of medical technology, it is now required to introduce a catheter into such a site as a smaller diameter vessel as found in the heart and brain. Diseases in cerebral vessels include aneurysm, arteriovenous malformation (AVM), and dual AVM. For inspection and treatment of such diseases, it is desired to have a catheter which can be inserted into a finer blood vessel or more peripheral blood vessel site.
However, the above-mentioned catheter has a main body portion made of a synthetic resin tube, which must have a certain wall thickness. It is thus inevitable that the outer diameter is increased by the extra wall thickness. Since the blood vessel into which the catheter can be introduced is restricted by its outer diameter, the catheter could only be introduced into a blood vessel sufficiently larger than the outer diameter of the catheter. If the catheter is made of a more rigid material, then the catheter as a whole is harder, leaving problems including the risk of the distal end causing damage to the vessel wall upon insertion and difficulty of insertion.
Therefore, another object of the present invention is to provide a novel and improved catheter which is reduced in wall thickness and hence, outer diameter and includes a fully flexible distal portion.